The present invention relates to a system and a method for handling multimedia conference calls in a telecommunication network.
Multimedia conferencing in telecommunication networks has been the subject of standardization efforts in a number of standardization organizations. For packet-based networks, ITU-T has produced a number of recommendations for multimedia communication under the umbrella recommendation H.323. The H.323 recommendation refers to a number of other recommendations such as the H.225.0 protocol that describes call signaling, media (audio and video), stream packetization, media stream synchronization, and control message formats, and the recommendation H.450 that describes supplementary services. Another signaling protocol is the Session Initiation Protocol (SIP) that has been specified by the IETF in the specification RFC 3261. RFC 3261 specifies a number of SIP messages, which carry the Session Description Protocol (SDP) specified in RFC 2327.
Currently, initiatives within the telecommunication community such as the Third Generation Partnership Project (3GPP) and 3GPP2 are specifying a next generation of packet switched core networks for telecommunication services. In 3GPP, a core network domain is called the IP Multimedia Subsystem (IMS). 3GPP is currently drafting requirements (e.g. 3GPP TS 22.173) including the support of a number of supplementary services in IMS. One example of a supplementary service is the multimedia conference (or a group call) where a plurality of multimedia terminals can be involved and where each terminal can support different media types. Media types are normally specified according the MIME standard (RFC 2046).
In addition, the Open Mobile Alliance (OMA) has defined standards for Push-to-Talk over Cellular (PoC). See, for example, Push to Talk over Cellular (PoC)—Architecture, draft version 2.0—March 2007, Open Mobile Alliance, OMA-AD_PoC-V2—0-20070326-D, which is incorporated herein by reference. The OMA PoC specifications set utilize a number of existing specifications from IETF, 3GPP, and 3GPP2, including the capabilities of the 3GPP IMS and 3GPP2 Multimedia Domain (MMD) to enable IP connectivity and IP based communication between mobile devices including multi-party conferencing.
In telecommunication systems such as IMS where calls are established and controlled by using SIP signaling, the SIP method called OPTIONS (described in IETF RFC 3261) may be utilized to determine a remote terminal's capabilities. The OPTIONS method enables a user terminal to query another user terminal or a proxy server as to its capabilities. This enables a client to discover information about the supported methods, content types, extensions, codecs, and the like without “ringing” the other party. The OPTIONS response is a so-called “200 OK” message with attached SDP, which describes the media support of the remote end. The 200 OK response message may also include feature tags showing other capabilities that could be of use to the sender of the OPTIONS request.